This invention relates to thermosetting injection molding machines for injection molding a natural or synthetic material that is cured by heating the material to a predetermined temperature. One problem which is encountered in the use of such machines is the relatively large amount of scrap material which may result from their use. When a large number of parts are to be produced with each cycle of the machine, the thermosetting material is pushed from an injector chamber under pressure to a mold which has interconnecting runners to distribute the thermosetting material from the injector chamber to each of the mold cavities. All of the thermosetting material which remains in the mold runners during curing is cured along with the material in the mold cavities. This material in the runners must then be scrapped as waste material.
The problem of wastage in thermosetting molding machines is not unknown. U.S. Pat. No. 3,661,487 relates to the problem of reducing the waste which is produced by thermosetting injection molding machines. U.S. Pat. No. 3,876,356 relates to the problem of reducing waste in thermosetting transfer molding machines.
Other prior art patents include U.S. Pat. No. 3,797,984, which relates to a single liquid cooled nozzle machine in which a sprue is formed in the tip of the nozzle. Prior art patents which disclose various distribution arrangements for thermo-plastic injection molding machines are shown in U.S. Pat. Nos. 2,871,517, 2,878,515 and 3,533,594.
The present invention departs from these and other machines by providing a thermosetting injection molding machine in which a large quantity of articles is produced with each cycle of the machine while the waste material is minimized. The machine includes a cold injector chamber, a cold distribution platen, an array of distribution nozzles having a zone of high temperature gradient from cold to hot, and a mold heating platen. The mold used in the machine has a plurality of hot mold cavities and a hot runner for each distribution nozzle. As used herein, the word "hot" refers to a temperature sufficient to substantially cure the thermosetting material within the machine cure cycle time. The word "cold" refers to a temperature below that required to substantially cure the thermosetting material during the allotted time, yet high enough that the thermosetting material flows properly and can be molded.
The invention further provides at least one straight distribution chamber extending laterally from edge to edge completely through the distribution platen, and a distribution nozzle blocking each end of the distribution chamber. Each distribution nozzle includes a core having a passage extending from the distribution chamber through the heating platen to its associated mold cluster. Each distribution nozzle also includes a jacket having a higher coefficient of thermal conductivity than the core surrounding the core and extending through the mold heating platen in spaced relation thereto and terminating at a location spaced from the end of the core passage. A bushing located at the tip of the core provides a seal between the heating platen and the tip of the core and maintains the thermosetting material in the tip of the core passage at a temperature of at least the curing temperature of the material. A short longitudinal space between the bushing and the jacket produes a zone of high temperature gradient so that the remaining portions of the passage in the core of the nozzle can be maintained at a temperature below the curing temperature of the thermosetting material. A system of cooling passages in the distribution platen maintains the temperature of a thermosetting material in the distribution platen below the curing temperature of the thermosetting material, and the heating platen maintains the temperature of the thermosetting material in each mold cluster at a temperature of at least the curing temperature of the material.
In this manner, a multiple nozzle distribution system and a mold heating system are provided by the thermosetting injection molding machine completely independently of the mold to simplify mold design. Additionally, the thermosetting material is delivered to an aray of several individual mold clusters by a distribution system which produces substantially no waste because all of the distribution system except the tip of the distribution nozzles is maintained at a temperature below the curing temperature of the thermosetting material. Still further, the hot runner of each mold cluster which conveys the thermosetting material from the distribution nozzle to the several mold cavities of the mold cluster is relatively short, since the runner need only connect the distribution nozzle with mold cavities which are close to one another and the runner need not connect all of the mold cavities of the mold. This minimizes the volume of thermosetting material in the hot runners of the mold and minimizes the waste produced in such runners when the material in the runners is cured.